Llanowar Reborn triggers "Whenever a creature enters the battlefield, you may move a +1/+1 counter from this land onto it." (Graft abilitie), all the time even when the +1/+1 counter was moved from
Llanowar Reborn to some creature.
Exemple: A Creature enters the battlefield, you choose to move a +1/+1 counter from
Llanowar Reborn to this creature. Then other creature enters the battlefield (the Graft abilitie of the
Llanowar will triggers again and if you choose yes nothing happens)
Moreover the description of this trigger (Graft abilitie of
Llanowar Reborn) in stack is =>
1. (OPTIONAL) Whenever another creature enters the battlefield, you may move a +1/+1 counter from this creature onto it.